AROUND 10am, the rain began to fall. It wasn’t especially heavy, but it was relentless. Hour after hour the downpour continued, soaking into the deep black soil. After midnight, the hill was saturated, and the water began to pool on the surface and run, carving a gully that deepened and flared as the rain continued.

A few weeks later, I am standing beneath that hill. Overhead, the sun shines in through a latticework of white metal bars. In front of me is the slush of black mud that washed onto the concrete floor, much to the consternation of the rain-makers. They hadn’t meant to carve out a chunk of the hillside – after all, they had only just built it.

Once, the giant glass chamber in which the storm took place was filled with sweet potato fields and rice paddies. It is part of a giant sealed complex of greenhouses built at the base of the Santa Catalina mountains north of Tucson, Arizona, which is home to a rainforest, savannah and even a miniature ocean. This is Biosphere 2, a facility built to prove that it was possible for humans to survive in a closed environment – with the help of some sunlight.

When a group of eight people were sealed into Biosphere 2 in 1991, the project was hailed as a groundbreaking scientific endeavour. The “Biospherians” were to live entirely on the food they grew, …